The invention relates to the area of damping, resistance generating, and motion control devices. Specifically, it relates to devices employing a controllable medium for damping, resistance generating, and motion control.
Dampers and shock-absorbers are known which use a hydraulic fluid as the working medium to create damping forces to control or minimize shock and/or vibration. Typically, the damping forces are generated by a pressures resisting movement between operative components of the damper or shock absorber. One class of these devices includes magnetorheological (MR) fluid devices. MR devices may be of the xe2x80x9crotary-actingxe2x80x9d or xe2x80x9clinear-actingxe2x80x9d variety. Known MR devices include linear dampers, rotary brakes, and rotary clutches. Each MR device employs a Magnetorheological (MR) fluid comprised of soft-magnetic particles dispersed within a liquid carrier. Typical particles include carbonyl iron, and the like, having various shapes, but which are preferably spherical and have mean diameters of between about 0.1 xcexcm to about 500 xcexcm. The carrier fluids include low viscosity hydraulic oils, and the like. In operation, these MR fluids exhibit a thickening behavior (a rheology change) upon being exposed to a magnetic field. The higher the magnetic field strength in the fluid, the higher the damping/restraining force or torque that can be achieved within the MR device.
MR fluid devices are disclosed in U.S. patent application Ser. No. 08/304,005 entitled xe2x80x9cMagnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Samexe2x80x9d, U.S. patent application Ser. No. 08/613,704 entitled xe2x80x9cPortable Controllable Fluid Rehabilitation Devicesxe2x80x9d, U.S. application Ser. No. 08/674,371 entitled xe2x80x9cControllable Brakexe2x80x9d, U.S. patent application Ser. No. 08/674,179 entitled xe2x80x9cControllable Vibration Apparatusxe2x80x9d and U.S. Pat. Nos. 5,547,049, 5,492,312, 5,398,917, 5,284,330, and 5,277,281, all of which are commonly assigned to the assignee of the present invention.
Known MR devices advantageously can provide controllable forces or torques, as the case may be, but, as currently designed, such devices are comparatively expensive to manufacture. These devices typically include a housing or chamber that contains a quantity magnetically controllable fluid, with a movable member, a piston or rotor, mounted for movement through the fluid in the housing. The housing and the movable member both include a magnetically permeable pole piece. A magnetic field generator produces a magnetic field across both pole pieces for directing the magnetic flux to desired regions of the controllable fluid. Such devices require precisely toleranced components, expensive seals, expensive bearings, and relatively large volumes of magnetically controllable fluid. The costs associated with such devices may be prohibitive to their use in certain applications, for example, washing machines and home exercise devices. Therefore, there is a long felt, and unmet, need for a simple and cost effective MR fluid device for providing variable forces and/or torques.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
The present invention provides a controllable medium device which uses a vastly reduced quantity of controllable rheological medium as compared to prior art devices, and which eliminates the need for expensive seals, bearings, and precisely toleranced components. As a result, the cost to manufacture such devices is dramatically reduced.
According to the invention, a small amount of controllable medium, preferably in fluid form, is entirely contained in a working space between relatively movable members subjected to the magnetic field by a fluid-retaining means, for example, an absorbent matrix (preferably an open cell foam or the like) or a wicking member. The inventor herein discovered that an absorbent member can hold a sufficient amount of fluid to produce a significant rheological effect between a first pole member and a relatively movable second pole member. The invention may be incorporated in various physical embodiments such as linear dampers, rotary dampers such as brakes, and mountings and applications therefor.
In particular, the present invention is a magnetorheological medium device which comprises first and second members coupled for relative movement and having a working space therebetween, means for producing a magnetic field that acts on the first and second members and the working space, and a field controllable medium contained substantially entirely in the working space.
A working space is provided by spacing the first and second members using structural supporting means. In a piston and cylinder device, for example, a working space is provided by selecting a piston head to have an outer dimension that is smaller than an inner dimension of the cylinder by a predetermined amount. The difference in size provides the working space when the piston head is assembled in the cylinder. In a piston and cylinder device, the structural support to maintain the spacing may conveniently be provided by a fluid retaining material surrounding and preferably fixed to the piston head. In a disk brake device, the working space is provided by mounting the rotor and caliper yoke in such a way as to space apart the surface of the rotor and the inner surfaces of the calipers.
According to a preferred embodiment of the invention, a controllable fluid is contained in the working space by a material providing an absorbent matrix disposed in the working space. Absorbent matrix is used here to indicate a material that has the ability to pick up and hold a fluid by wicking or capillary action. In a particularly preferred embodiment, the absorbent matrix is a sponge-like material, for example, an open-celled or partly open-celled foam. Polyurethane foam and rubber foam are examples of particularly suitable materials. Foams made of other materials are also suitable, and examples include silicone rubber, polyamide, viton rubber, neoprene, loner rubber, melamine, a polyimide high temperature foam, and metal foams.
An absorbent matrix can also be formed of other material structures, such as an unwoven material, such as mineral wool, or a felt, for example, Nomex brand aramid fiber felt or a compressed carbon fiber felt. In addition, a woven fabric could be used, made from materials such as KEVLAR brand fiber, graphite, silica, NOMEX brand aramid fiber, polybenzimadazole, TEFLON brand fiber, and GORE-TEX brand fiber. Alternatively, a mesh material, such as a metal mesh, could be used.
Other structures that can contain a fluid, for example, brushes, flocked surface materials, wipers, and gaskets are also suitable.
The absorbent matrix need not entirely fill the working space, as long as the field controllable medium is contained in the working space. Thus, the absorbent matrix may be formed as a structure having a plurality of cavities, such as a honeycomb or other network structure, to contain the medium in the working space.
Alternatively, in a linear acting damper, the fluid retaining means can be disposed as dams or wipers at end regions of the working space, leaving an open center region, the dams sliding with a linearly moving member relative to a fixed member for retaining the controllable medium in the working space.
By containing an effective amount of controllable medium only in the working space of the device, no expensive seals are needed to contain the controllable medium as in the prior art.
It is another advantage of the invention that amount of controllable medium needed to accomplish the rheology-based resistance effect is dramatically reduced to only the amount contained in the working space.
Another advantage of the invention, is providing a linear damper that requires no seals or bearings.
Another advantage of the invention, is providing a linear damper that doesn""t require precisely toleranced components, i.e., non-ground piston rods and loosely toleranced outer member tubes and pistons.
According to the invention, means for generating a field in the first and second member and the working space is mounted to either of the first or second members in proximity with the working space. For example, in a piston/cylinder damper, the generating means can be at least one coil circumferentially wrapped on the piston head. In a rotary damper, the generating means can be at least one coil mounted to a yoke having arms between which the rotor turns.
A damping device in accordance with the invention can be incorporated in a number of apparatuses where it previously was cost-prohibitive to use controllable dampers. For example, the dampers of the invention can be used in washing machines to control vibration during various cycles. A resistance device of the invention can also be incorporated in exercise devices, such as bicycles, step machines, and treadmills to provide variable resistance.
The above-mentioned and further features, advantages, and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings.